No-one was to blame for missing an unexploded bomb during survey works in a Great Yarmouth riverbed, an investigation has found.

An unexploded bomb, weighing 250kg and believed to be from the Second World War, was discovered by a contractor working on the third river crossing development in February.

Roads on both sides of the site were cordoned off, and rest centres were opened to allow evacuated residents a place to stay.

Great Yarmouth Mercury: The sand wall being built around the device. Image: Oliv3r Drone PhotographyThe sand wall being built around the device. Image: Oliv3r Drone Photography (Image: Oliv3r Drone Photography)

The bomb detonated shortly before 5pm on February 10, during a slow burn procedure intended to disarm the bomb.

There were no injuries, but Bollard Quay's wall was damaged. 

Great Yarmouth Mercury: An unexploded bomb close to Johnson and Sons on Southgates Road. Image: GYBCAn unexploded bomb close to Johnson and Sons on Southgates Road. Image: GYBC (Image: GYBC)

The blast followed a four-day ordeal which saw bomb disposal experts make several attempts to defuse the bomb safely, and a 400-tonne sandblast barrier was built around the device.

Following the detonation, an investigation was launched to assess why the unexploded bomb had not been identified earlier during the construction of the Herring Bridge.

Great Yarmouth Mercury: The Herring Bridge's second leaf bascule being tugged down the River Yare. Picture - Luke Martin PhotographyThe Herring Bridge's second leaf bascule being tugged down the River Yare. Picture - Luke Martin Photography (Image: Luke Martin Photography)

Tony Mulholland, project director at BAM Farrans Joint Venture said: "Our investigation found all appropriate checks and surveys were carried out which clearly showed there were no unidentified objects highlighted within the works areas at that time.

"As a result of the explosion, further repairs and strengthening of the quay wall will be carried out later this year.

"We do not anticipate these works will prevent the bridge from becoming fully operational later this summer."

Earlier this week, Mr Mulholland confirmed the third river crossing's eastern approach embankment on South Denes Road and the associated underpass have been completed. 

Part of the road has been widened, and a new signal-controlled junction has been installed.

The development will now focus on the western approach embankment and its connecting roundabout by William Adams Way and Suffolk Road.

There are also plans for the third and final river possession to enable the lowering of the bridge for testing and commissioning and to add road markings to each bridge leaf.